This invention relates to a magnetic recording and reproducing device and, more particularly, to a rotary head type magnetic recording and reproducing device such as an R-DAT (rotary head type digital audio tape recorder) capable of reading information recorded on a recording tape in a stable manner during fast feeding or rewinding of the recording tape.
The R-DAT is a device which converts analog signals such as an audio signal into PCM signals, records the PCM signals on a magnetic tape and reproduces the same.
As shown in FIG. 2, the device comprises a rotary head 2 having two magnetic heads A and B separated by 180 degree interval on the circumferential surface of a cylinder 1. A tape 3 is loaded from a casette housing 4 with a vertical post 5 or with an inclined post 6, wound on the circumferential surface of the rotary head 2 for 90 degrees, supported by a fixed guide 7, and run by a capstan 8 and a pinch roller 9.
The diameter of the rotary head 2 is 30 mm, and the winding angle for the tape is 90 degrees. For recording and reproduction, at the mode I which is usually used, the rate of the rotary head 2 is 2,000 rpm (circumferential speed: 3.14 m/sec) and the speed of the tape 3 at 8.15 mm/sec in the direction identical to that of the rotary head 2. The relative speed of the head 2 as against the tape 3 is 3.13 m/sec.
The recording system with R-DAT is a helical scanning azimuth recording. Its tape format as shown in FIG. 3 defines with the track angle of 6.degree. 22' 59.5" and azimuth angle of .+-.20.degree. with the tracks alternately traced by two heads A and B.
FIG. 4 shows a track format wherein audio data are recorded at the center of a PCM region, and sub-codes and control signals such as ATF (automantic track finding) are recorded on both sides thereof.
The PCM region comprises 128 blocks as shown in FIG. 5 each of which has recording regions for a block synchronizing (indicating the starting position of the block), ID (identification) code, block address, parity check code, and audio data. At the mode I, audio data uses 2's complement codes of quantization bit of 16 bits of the sampling frequency of 48 kHz, and the PCM data is divided into 8 bits in higher order and 8 bits of lower order, modulated from 8 bits into 10 bits (8-10 modulation) and recorded in 10 bits.
In the sub-code region (8 blocks), data such as music number and time data are recorded. An example of a format in the sub-code region (for one block) is shown in FIG. 6.
For tracking control during reproducing in the R-DAT, an automatic tracking system with ATF is employed. ATF system detects and compares crosstalks from two adjacent tracks by ATF signals (FIG. 4) recorded on the tracks, and controls the speed of the capstan motor for running tape so as to make crosstalks identical. By this arrangement, the head A is caused to trace a track whose azimuth is +20.degree. (hereinafter referred to as A track) and the head B is caused to trace a track whose azimuth is -20.degree. (hereinafter referred to as B track). These heads A and B can respectively trace a width which is about one and half times each track width.
In a magnetic recording and reproducing device such as R-DAT, it will be very convenient if information recorded on the tape can be reproduced even partially during fast feeding (feeding of the tape at a speed which is higher than a normal playback speed) or rewinding (feeding of the tape in a reverse direction to the normal playback direction).
In an R-DAT, for example, it is important for designing the system as a convenient one to have capability of reading data such as present music number and time information recorded on the sub-code region during search (i.e., operation for detecting a desired music number or position in the music). Particularly, in fast search which is conducted at a high speed such as 200 times as fast as the normal speed, it will be extremely difficult to detect a desired tape position unless such data can be read in a stable manner.
In fast search in an R-DAT, the head traces plural tracks, crossing these tracks obliquely as shown in FIG. 7 and passes over a sub-code region of one of these tracks in one crossing. If the relative speed between the head and tape is deviated largely from predetermined relative speed (3.13 m/sec in the case of R-DAT), reproduction of clock cannot be made even if a signal is obtained from the head and, as a result, a sub-code cannot be read. For reading a sub-code, it is necessary for the relative speed between the tape and head to be within a range in which clock can be reproduced (i.e., range in which the relative speed can be subjected to the PLL control for reproduction of clock).
It is, therefore, an object of the invention to provide a magnetic recording and reproducing device capable of adjusting, with a simple construction, the relative speed between the tape and head during fast search conducted at a speed of, for example, 200 times as fast as the normal speed.